62 national geographic • December 2016
worked on hormones in wild apes,” she says.
“People said I was crazy.”
Knott’s studies have special significance be-
cause female orangutans give birth only every six
to nine years. No other mammal has a longer in-
terval between births. And there’s no telling what
her research might mean for our knowledge of
human fertility; we and orangutans are so similar
that Knott can use standard drugstore test kits
on urine from female orangutans to determine
whether they’re pregnant.
Typical of many forests in southeastern Asia,
the trees at Gunung Palung produce little or no
fruit in most seasons. Then, every four years or
so, trees of various species simultaneously bring
forth massive amounts of fruit in a process called
masting. The phenomenon led Knott to wonder
about the connection between food abundance
and orangutan reproduction.
Knott discovered that researchers could col-
lect and preserve urine from female orangutans
on filter paper so that the samples could be tested
for hormones later. Her work has shown that re-
productive hormones in female orangutans peak
when fruit is most abundant in the forest—an
adaptation to the boom-and-bust environment.
Cheryl Knott tells me as we sit beneath the rain
forest canopy at her orangutan research station
in western Borneo. The high-pitched, dental-
drill sound of cicadas fills the air, at times forcing
us to pause our conversation. As we talk, Knott’s
associates are at work in the surrounding forest
of Indonesia’s Gunung Palung National Park
with GPS units and iPads, following orangutans
in their daily wanderings, recording what they’re
doing, what they’re eating, and how they’re in-
teracting with others of their species.
Unlike gorillas and chimpanzees—fellow great
apes that live in groups and can be followed and
observed relatively easily—orangutans live most-
ly solitary lives. They spend nearly all their time
in the treetops, they wander widely, and for the
most part they inhabit rugged forest or swampy
lowland that’s hard for humans to traverse. As
a result, orangutans long remained among the
least known of Earth’s large land animals. Only
during the past 20 years or so has scientific evi-
dence begun to outweigh speculation as a new
generation of researchers has tracked the elusive
apes across the islands of Borneo and Sumatra,
the only places orangutans live.
For more than two decades Knott has super-
vised the research at Gunung Palung, looking at
many aspects of orangutan life history but fo-
cusing especially on the way the availability of
food affects female hormones and reproduction.
“At the time we started here, no one had really
By Mel White
Photographs by Tim Laman
An 11­month­old baby copies mom at mealtime. The
juvenile will stay with its mother for up to 10 years as
she passes on essential survival skills. Among them:
how to find the most nutritious rain forest fruits.
‘Sometimes I feel like I’ve
chosen the most difficult
thing in the world to study,’